Method of font rendering employing greyscale processing of grid-fitted fonts

Claim 1

A method in a computer system (15) of displaying a character on a pixel oriented gray scale display device (17) having a predetermined resolution by constructing a pixel map comprising the steps of: providing (71) a geometric descriptor in a normalized character space for said character; receiving (66) from an application (19) a requested character space height and data specifying said predetermined resolution; scaling (72) said geometric descriptor to provide a scaled geometric descriptor in physical pixel coordinates as a function of said predetermined resolution and said requested character space height; determining (67) a character space height value P, in physical pixel units, from said requested character space height and said data specifying said predetermined resolution; said method characterized by the steps of: comparing (75,79) said character space height value P to selected values J and K, J and K each being positive integers and J being less than K; and (a) if P is less than J, performing a gray-scale rendering of said character by: subdividing (82) at least all physical pixels that are at least partially within stroke of said scaled geometric descriptor into N subpixels, N being an integer; performing (85) a scan conversion on said scaled geometric descriptor with respect to said subpixels to provide a binary subpixel bit map of on-subpixels and off-subpixels; for each said physical pixel that is at least partially within a stroke of said scaled geometric descriptor, assigning (88) a gray scale value in accordance with the number of said on-subpixels it contains; and displaying (96) said physical pixel on said display device using said gray scale value; (b) if P is greater than or equal to J and less than or equal to K: providing (78) a hinted scaled geometric descriptor by hinting said scaled geometric descriptor so that boundaries of serifs and stems lie on boundaries of physical pixels; performing (91) a scan conversion on said hinted scaled geometric descriptor to provide a binary pixel bit map of on-pixels and off-pixels; displaying (96) each said physical pixel on said display device using a maximum gray scale value for pixels corresponding to said on-pixels in said binary pixel bit map and using a minimum gray scale value for pixels corresponding to said off-pixels in said binary pixel bit map; and alternately (c) if P is greater than K: providing (78) said hinted scaled geometric descriptor by hinting said scaled geometric descriptor so that boundaries of serifs and stems lie on boundaries of physical pixels; and performing (88) said gray-scale rendering of said character with respect to said hinted scaled geometric descriptor.